Optical Momentum Alignment Effect in WSe₂ Phototransistor

Abstract The optical momentum alignment effect is demonstrated in WSe₂ phototransistors . When the photon energy is above the A exciton energy, the maximum photocurrent response occurs for the light polarization direction parallel to the metal electrode edge, suggesting that electrons in the valence band of WSe₂ prefer to absorb photons with the polarization direction perpendicular to their momentum direction. Further studies indicate that the anisotropic distribution of photo‐excited carriers is likely due to the pseudospin‐induced optical transition selection rules. If the photon energy is below the A exciton energy, the photocurrent signals are maximized when the incident light is polarized in the direction perpendicular to the electrode edge, which is mainly attributed to the polarized absorption of the plasmonic gold electrodes. Moreover, the photocurrent peak can be controlled by an electric field via the quantum confined Stark effect. This resonance peak can also be shifted by adjusting environmental temperatures due to the temperature‐dependent nature of the WSe₂ band gap. These experimental studies shed light on the knowledge of photocurrent generation mechanisms, opening the door for engineering future anisotropic optoelectronics.